1. Field of the Invention
This invention relates to an apparatus for determining the location of an electrostatic discharge event (ESD).
2. Description of Related Art
Some electrostatic discharge events (ESD) are of such a low level as to be virtually imperceptible to human beings, even though these discharges may cause significant damage, such as to electronic devices. Detectors have been invented which are capable of detecting the occurrence of such an ESD event but which are incapable of determining its location. An example of such a system is disclosed in U.S. Pat. No. 4,631,473 issued to Masamitsu Honda on Dec. 23, 1986 and entitled "Transient Electromagnetic Field Detector".
A device which is capable of actually pin-pointing the location of an ESD event has been achieved in U.S. Pat. No. 5,923,150, issued to DeChiaro et al., entitled "Electrostatic Discharge Event Locators" (the EELS system) which was filed Apr. 19, 1997 and issued Jul. 13, 1999 and which is hereby incorporated in total by reference. This EELS system achieves great precision in determining the ESD location within a cube of 5 mm in dimension. This precision is attained at the expense of elaborate electronic circuitry, including expensive high speed analog-digital converters that need a high speed clock to drive the system.
There are many applications where the need for the precision of locating the ESD event lies between the above two approaches. That is, more that just a determination that an ESD event occurred is needed yet the 5 mm precision and corresponding cost of the EELS system is not warranted. For example, one may like to know if there are ESD events that are originating from a volume of space, for example, 2 m.times.2 m.times.10 m in dimension, where sensitive electronic circuit boards are being assembled. Another example would be a 2 m.times.2 m.times.6 m area in which sensitive equipment was being operated. Still another example would relate to protection of life and property by determining if there were ESD sparks occurring in an area where flammables or explosives are present.
In addition to the above determinations as to a volume of space, there may exist situations in which it is only necessary to evaluate an open ended area, for example, 2 m.times.4 m in dimension, regardless of the vertical location of the events. Still even simpler would be an application in which it is only necessary to determine if a given ESD event comes from the right or left sides of a planar surface.
For each of these cases, the 5 mm precision of a locating system such as the EELS system is not necessary, and in light of its associated costs, is not desired. The present invention addresses these cases in achieving sufficient accuracy in determining the location of the ESD event at a significantly reduced cost.